Surface-water-quality dynamics in the Mekong Delta: impacts of pollution sources and altered flow regimes
Abstract
The Mekong Delta is experiencing surface-water-quality degradation driven not only by increasing pollution loads but also by altered flow regimes, salinity intrusion, sediment starvation, and shifting hydraulic operation. This paper synthesizes and analyzes monitoring records for 2016–2024, a database of 3,117 samples, supplementary surveys conducted in 2022–2024, and hydrodynamic–salinity–morphological studies to clarify surface-water-quality dynamics in the Mekong Delta through two linked dimensions: the direct impacts of pollution sources and the amplifying role of altered flows. The analytical framework combines descriptive statistics based on WQI, PCA/FA/AHC for identifying major pollution components, and ESAT/MixSIAR for source apportionment. Results show that WQI ranges from 2.376 to 85.314, with a regional mean of 47.486; high-risk hotspots are concentrated in coastal zones, peri-urban reaches, areas of intensive aquaculture, and canals with poor water exchange. Five major pollution components are identified: organic pollution associated with domestic and industrial wastewater; agricultural runoff and pesticides; microbial contamination linked to Zn/Cu; salinity-related mobilization of As and Cr; and combined nutrient–microbial pollution. Source apportionment indicates that domestic and industrial discharges dominate urban and estuarine corridors, whereas agriculture and aquaculture are more influential in inner-delta and coastal settings. Altered flows do not create pollutants directly, but they reduce dilution capacity, increase water residence time, deepen salinity intrusion, and enhance pollutant remobilization. In the Soc Trang area, dry-season surface water may contain up to about 29.5% seawater, while in the Tien River low-flow water levels can decline markedly even when dry-season discharge increases, highlighting the role of channel-bed incision in water-quality risk. The study recommends integrated management of water quality, pollution sources, flows, and salinity by subregion and season.